Science Buddies: "Ask an Expert"

Hi I am just after some guidance on the variables to a fair test. I have included my fair test below and I am wondering if I am correct on the variables. Or would be using the five different brands of aspirin be like having two independent variables? Should I only use one brand of aspirin?

Research question: Does the temperature of water effect the way different brands of aspirin dissolve in water?

Five different brands of aspirin will be submerged into water of the same temperature and volume to determine which of the five different brands of aspirin will dissolve the fastest in the different temperatures. Each of the five different brands will be tested individually in each of the three differing temperatures (hot, room temperature and ice cold). The temperature for each of the individual tests will be measured to ensure that the temperatures are equal. Time will be measured from as soon as the aspirin touches the water and will be measured until the aspirin is dissolved in the water (there may be some tiny particles seen in the water, but all visible signs of dissolution will have finished).

Independent Variable: The temperature of the water being used. (Boiling, room temperature and ice cold)

Dependent Variables: Time taken for each aspirin to dissolve in the different temperatures of water.

Controlled Variables:
• The same size and brand of cup used.
• The amount of aspirin used. (All the same weight).
• Temperature of the water for each test.
• All tests will begin as soon as the aspirin touches the water.
• All tests will conclude as soon as the aspirin has finished dissolving. (Some tiny particles may still be seen but all visible signs of dissolving have finished.)
• One person conducting the experiment.
• Using the same stop watch for each test to ensure all measured times are accurate.

Hypothesis: As the temperature of the water increases the dissolution times of each brand will increase.

Any advice would be greatly appreciated

Hi Danika280984 -

I believe you you have identified the independent and dependent variables correctly. However, I also believe that your hypothesis is flawed. Since most substances dissolve faster in warmer water, you may want to relook at this.

Regards,
Gerry

Hello,

I agree with Gerry that dissolution time would decrease (rate would increase) as water temperature increases.

Also, it does seem like you are trying to test out two different independent variables at once--both temperature and brand of aspirin. It is possible to test out both, in that case you may want to say something about how different brands might affect dissolution time in your hypothesis as well.

I would actually be very interested to know whether different brands of aspirin would dissolve at different rates. If you decide to test this as well, you may want to look up composition of aspirin of the various brands. The amount of active ingredient (acetylsalicylic acid) present in each tablet may be different in different brands; or maybe some of the inactive ingredients can interact at different rates with water molecules, thus causing different rates of dissolution.

Maybe you can do a two part experiment, something like:
(1) One brand of aspirin only, 5-10 different temperatures
(2) Same temperature, 5 different brands

Note that by changing only one thing at a time, it is easier to see any correlation between the independent and dependent variables.

Hey,

Interesting study. The answer to your stated question, "Does the temperature of water effect the way different brands of aspirin dissolve in water?" does require the inclusion of both temperature and brand in your experiment. And yes, both are independent variables.

In the end, you will have a table similar to below:

Time to Dissolution (hrs)
Temp Brand A Brand B Brand C
0C 17 18 19
25C 6 8 10
100C .2 .5 .8

For each brand, you will have a Temp vs Time curve. Plot all curves on the same graph. If they end up right on top of each other, the answer to your question is a resounding "No"

However, I anticipate that there will be some differences, in which case the answer to your question is "Yes" Now the hard part...why does this happen and what does this mean?

So dissolving stuff in a fluid depends upon the chemistry of the system. Fundamentally, chemical reactions follow Arrhenius where time and temperature are sort of like approximately equivalent. For example more time at lower temp is approximately equivalent to less time at higher temp. Note this only holds for a single chemical reaction (which we can approximate for this study).

So if all curves fell right on top of each other, we can say they most likely have very similar chemistry (ie, have very similar binders, carriers, etc). If the curves are separated, then we can say they most likely have different chemistries. Then I would take a look at the listed INACTIVE ingredients, find their molecular structures (look for active groups that like water like OH or CO and such) and hypothesize as to why they dissolved faster (lots of active groups that like water) / slower (less active groups) then the next one.

Would be interested in seeing the results